New research opens doors to the practical use of quantum light in advanced manufacturing, quantum computing, and more
esearchers from the University of Sydney and the University of Basel in Switzerland have made a groundbreaking breakthrough in quantum technologies by demonstrating their ability to manipulate and identify small numbers of interacting photons with high correlation. This remarkable achievement, published in the esteemed journal Nature Physics, marks the first time that scientists have been able to observe stimulated emission, which was postulated by Einstein in 1916, for a single photon.
Stimulated emission is widely observed for large numbers of photons and is the basis for the invention of the laser. However, this research takes it a step further by showing that stimulated emission can be observed for single photons. The scientists were able to measure the direct time delay between one photon and a pair of bound photons scattering off a single quantum dot, which is a type of artificially created atom.
This unprecedented milestone represents a significant step forward in the development of quantum technologies, which have the potential to revolutionize computing and communication.
“This opens the door to the manipulation of what we can call ‘quantum light’,” remarks lead author Dr. Sahand Mahmoodian.
“This fundamental science opens the pathway for advances in quantum-enhanced measurement techniques and photonic quantum computing.”
More than a hundred years ago, scientists made a groundbreaking discovery about light that changed our understanding of it forever. By observing how light interacted with matter, they realized that it was neither solely a beam of particles nor solely a wave pattern of energy. Instead, light exhibited both characteristics, a phenomenon known as wave-particle duality.
Since then, the study of how light interacts with matter has continued to captivate scientists and spark the human imagination. This research has not only enriched our understanding of the universe at a fundamental level but also led to practical applications with powerful implications.
From the way light travels through the vast expanses of the interstellar medium to the development of the laser, the study of light is a critical field with significant practical uses. Without this research, practically all modern technology that we take for granted today – including mobile phones, global communication networks, computers, GPS, and modern medical imaging – would be impossible.
The use of light in communication, specifically through optic fibers, offers a significant advantage over other methods because photons, the packets of light energy, do not interact with each other easily. This feature enables the transfer of information at the speed of light with minimal distortion.
However, there are instances where we need light to interact with other particles. This situation poses a challenge.
For example, interferometers use light to measure small changes in distance, and these instruments have become a common sight in modern advanced medical imaging. They are also used for more mundane tasks such as quality control checks on milk or for sophisticated instruments like LIGO, which detected gravitational waves for the first time in 2015.
The sensitivity of such devices is subject to constraints imposed by the laws of quantum mechanics. These constraints depend on both the average number of photons present in the measuring device and the degree of sensitivity that can be achieved. Notably, the limits differ for classical laser light as compared to quantum light.
“The device we built,” says lead author Dr. Nathasha, “induced such strong interactions between photons that we were able to observe the difference between one photon interacting with it compared to two.
“We observed that one photon was delayed by a longer time compared to two photons. With this really strong photon-photon interaction, the two photons become entangled in the form of what is called a two-photon bound state.”
In principle, quantum light has an advantage over other forms of light, as it can enable more precise and sensitive measurements while using fewer photons. This can be especially valuable in biological microscopy, where high light intensities can harm samples and the features under examination may be extremely small.
“By demonstrating that we can identify and manipulate photon-bound states, we have taken a vital first step towards harnessing quantum light for practical use,” adds Dr. Mahmoodian.
“The next steps in my research are to see how this approach can be used to generate states of light that are useful for fault-tolerant quantum computing, which is being pursued by multimillion dollar companies, such as PsiQuantum and Xanadu.”
“This experiment is beautiful, not only because it validates a fundamental effect – stimulated emission – at its ultimate limit,” remarks Dr. Tomm, “but it also represents a huge technological step towards advanced applications.
“We can apply the same principles to develop more-efficient devices that give us photon bound states. This is very promising for applications in a wide range of areas: from biology to advanced manufacturing and quantum information processing.”
The University of Basel, Leibniz University Hannover, the University of Sydney, and Ruhr University Bochum collaborated on the research project. Dr. Natasha Tomm of the University of Basel and Dr. Sahand Mahmoodian of the University of Sydney, where he serves as an Australian Research Council Future Fellow and Senior Lecturer, are the lead authors. The quantum dots, or artificial atoms, used in the experiment were produced at Bochum and employed in the Nano-Photonics Group at the University of Basel. Theoretical work related to the discovery was conducted by Dr. Mahmoodian at the University of Sydney and Leibniz University Hannover.